Cancer metastasis is a leading cause of death for patients having solid-tumor cancers. Circulating tumor cells (CTCs) are tumor cells disseminated from the primary tumor into the bloodstream during metastasis. The presence of CTCs in peripheral blood has important clinical significance for early cancer diagnostics and patient treatment monitoring. Study of CTCs will also provide a valuable insight into the mechanism of tumor metastasis.
Most current CTC assays are either used for the enumeration of CTCs by immunostaining (Paterlini-Brechot, et al. Cancer Lett., 2007, 253, 180-204; Zheng, et al. J. Chromatogr., A, 2007, 1162, 154-161; Nagrath, et al. Nature, 2007, 450, 1235-1239; Helzer, et al. Cancer Res., 2009, 69, 7860-7866; Talasaz, et al. Proc. Natl. Acad. Sci. USA, 2009, 106, 3970-3975; Gleghorn, et al. Lab Chip, 2010, 10, 27-29), or for specific molecular analysis by quantitative PCR (qPCR) (Fizazi, et al. Ann Oncol, 2007, 18, 518-521; Xu, et al. Cancer Res., submitted). For both applications, the main challenge is the extremely low concentration of CTCs (e.g. ˜1/mL) in the patient peripheral blood. Therefore, an enrichment step of rare CTCs from a large volume (e.g. in the milliliter range) of patient blood sample is crucial for successful CTC study. Size based filtration has been explored for solid-tumor cancers because epithelial CTCs (15-30 μm in diameter) are generally much larger and less deformable than normal blood cells (Paterlini-Brechot, et al. Cancer Lett., 2007, 253, 180-204; Zheng, et al. Chromatogr., A, 2007, 1162, 154-161; Xu, et al. Cancer Res., submitted; Vona, et al. Am. J. Pathol., 2000, 156, 57-63; Kahn, et al. Breast Cancer Res. and Treat, 2004, 86, 237-247; Zabaglo, et al. Cytometry A, 2003, 55, 102-108; Chen, et al. Surf. Interface Anal., 2006, 38, 996-1003; Tan, et al. Biomed Microdevices, 2009, 11, 883-892; Kuo, et al. Lab Chip, 2010, 10, 837-842; Mohamed, et al. J. Chromatogr., A, 2009, 1216, 8289-8295).
Among various filter designs, membrane filters have the advantage of large efficient filtration area, which usually means short operation time (i.e. high throughput) (Paterlini-Brechot, et al. Cancer Lett., 2007, 253, 180-204; Zheng, et al. J Chromatogr., A, 2007, 1162, 154-161; Xu, et al. Cancer Res., submitted; Vona, et al. Am. J Pathol., 2000, 156, 57-63; Kahn, et al. Breast Cancer Res. and Treat, 2004, 86, 237-247; Zabaglo, et al. Cytometry A, 2003, 55, 102-108). Both commercial track-etched polycarbonate membrane filters and micromachined parylene membrane filter with circular pores were previously reported and have been used in clinical trials for CTC detection. However, one major problem of the single-layer membrane filters is that fragile CTCs are easily damaged or even lysed during the filtration process, resulting in detection failure. For this reason, these works mainly focused on pre-fixed cells (Paterlini-Brechot, et al. Cancer Lett., 2007, 253, 180-204; Zheng, et al. J. Chromatogr., A, 2007, 1162, 154-161; Vona, et al. Am. J. Pathol., 2000, 156, 57-63; Kahn, et al. Breast Cancer Res. and Treat, 2004, 86, 237-247; Zabaglo, et al. Cytometry A, 2003, 55, 102-108), which disallowed further biological analysis requiring viable cells, such as genetic and chemotherapy studies, as well as cell culture applications. To address this problem, dual-layer 3D parylene membrane filters were reported for live capture of CTCs (Zheng, et al. Proc. of Hilton Head 2008, Hilton Head Island, S.C., USA, 2008, 134-137; Lu, et al. Proc. of μTAS 2009, Jeju, Korea, 2009, 588-590). Although they were able to maintain high viability of captured CTCs, the enrichment was too low because too many blood cells were trapped inside the filter gap.
Understanding the underlying biomechanics of viable CTC capture by filtration is of fundamental importance. However, by far most reports on CTC capture only focus on the design, testing and clinical trials of various kinds of special filtration devices. Only a few studies have been devoted to the fundamental work (Kuo, et al. Lab Chip, 2010, 10, 837-842.). Kuo et al. used an analytical method to study the biophysics of filtration, with emphasis on the pressure experienced by cells under various hydrodynamic environments during lateral-flow filtration (Kuo et al.). However, some important topics, such as the optimal filter geometry size, the safe range of transfilter pressure or inflow rate, and the quantitative measurements of enrichment and viability, are not provided.
Therefore, there remains a need to develop methods and systems that are capable of simple, yet highly efficient capturing of live tumor cells with high viability to overcome the above shortcomings. The present invention satisfies these and other needs.